Manufacture of tube element



Nov. 1, 1966 F STORK ETAL 3,282,762

MANUFACTURE OF TUBE ELEMENT Filed June 20, 1962 9 -8 Fig.1

8 1 x: g 14 fig} 7 ATTORNEY United States Patent 15 Ciaims. (Cl. 156253) The present invention relates generally to the art of making elements for electrical discharge tubes, and, more particularly, to the manufacture of a flat cathode for electrical discharge or vacuum tubes which is provided with a coating of an oxide of an alkaline earth metal.

The oxide coatings of such cathodes, particularly when used in special purpose tubes, must conform to high standards with respect to the thickness, uniformity of the coating up to the edges thereof, and with respect to a sharp or accurate demarcation or boundary of the coating.

With the methods which have been previously used for producing oxide cathodes the production of sharply demarcated coatings of constant thickness can be produced, if at all, only with great difiiculties. For example, known methods include providing the alkaline earth-carbonate coating by means of sputtering, depositing sediment, coating, cataphoresis and the like, and also by subsequent working or pressing of the coating.

With there defects of the prior art in' mind, it is a main object of the present invention to provide for the manufacture of oxide layers on cathode holders, which layers are of predetermined thickness up to their edges, whereby the edges will be sharply demarcated or defined.

Another object of the instant invention is to provide a method and apparatus for constructing a cathode of the type described, in a simple and efiicient manner.

A further object of this invention is to provide a method of constructing a fiat cathode wherein damage to the emission foil is prevented.

These objects and others ancillary thereto are accomplished according to preferred embodiments of the invention wherein the known process i used as a starting point in the manufacture of a flat cathode for electrical discharge tubes which cathode is constructed of foil containing alkaline earth carbonates and is mounted on the cathode holder. According to the present invention, a section of the foil of the necessary size is punched out, and then, in the same step, this section is placed onto the surface of the cathode holder using the punching device which carries out the punching step. Thus, within the same working step as the punching proper, the punched out foil is placed or pressed onto the surface of the cathode holder. The emission or cathode foil is constructed of an alkaline earth carbonate and a synthetic such as, for example, an n-butyLmethacrylate. Such a construction of an emission foil is known.

The punching of the foil and the mounting ofthe foil section onto the surface of the cathode carrier is performed in a single step and thus damage to the emission foil proper can no longer occur.

In this manner, the

emissive coating is produced of constant thickness and with sharply demarcated or delineated edges.

The punch of the punching apparatus may be used either to actually press the punched out foil tightly onto the cathode holder, or may be used for placing this foil onto the surface of the cathode holder. In the latter event, the surface of the cathode holder is first to be coated with a non-drying sticky film of a solution of a synthetic. This solution of the synthetic should comprise a material which decays or decomposes once the cathode is activated and which does not provide a residue which causes cathode poisoning. This latter step of using a film for holding the foil to the cathode holder is preferred if a pressing operation is to be avoided.

The same process may be used for producing annular cathodes or cathodes having annular emission surfaces. When such a cathode is to be produce-d a hole is first punched into the foil by means of a punching device having a removable die. Then, the die is removed and the cathode holder is put in its place, this being done after the hole is punched. Next, with the aid of the punch proper, which is larger than the punch creating the abovementioned hole, the punch removes the section of foil surrounding the hole and which is of appropriate size for the cathode in order to provide an annular-shaped foil. After the foil is punched out, it is then glued or pressed onto the cathode holder.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic view of a punching apparatus for forming one type of cathode.

FIGURE 2 is a schematic view illustrating a punching apparatus in the first step thereof for providing another form of cathode.

FIGURE 3 is a schematic view of the punching apparatus of FIGURE 2 in another step of the procedure in forming this other embodiment of cathode.

With more particular reference to FIGURE 1, a device is illustrated which is used for producing a flat cathode. This punching device includes a punch 3 which moves through an internal opening 8 formed in the die 4. The cathode holder 2 may be inserted into opening 8 from below. A foil 1 of an alkaline earth carbonate material is placed on top of the die 4 and in a single working or operational step a piece of this foil corresponding to the diameter of the punch proper is punched from the foil due to a shearing action between the punch 3 and the upper edges of the opening 8 in the die 4. Further movement of the punch 3 may be used to press the foil to the front or upper surface of the cathode holder 2.

In the event that the foil is to be glued to the cathode holder 2, then this upper surface is first provided with a glue film and the punch 3 is moved downwardly in such a manner that the foil is gently brought into contact with this surface of the cathode holder 2. When manufacturing a cathode in such a manner, it is advisable to provide a stop for the punch 3 in order to prevent excessive pressing of the foil onto the cathode holder.

Synthetic glues which have proven advantageous for use as the film of glue for holding the foil to the holder include glues of the poly-iso'butylene, the polyacrylic acid ester, or of the poly-methacryl-ic acid ester type. Preferably this synthetic glue is provided having a thickness of 110,LL.

FIGURES 2 and 3 illustrate an example of a device for forming an annular or ring-type cathode, i.e., a cathode having an annular emission surface. This type of cathode is used in electron guns in order to provide a hollow electron beam. With such cathodes emission primarily takes place from the outer edges of the surface and for this reason it is particularly necessary that the outer edge of the emission surface be sharply delineated or demarcated. Under no circumstances may the uniformity of this edge be interrupted due to spaces which may perhaps be caused by broken particles of glue or the like.

According to the device of FIGURES 2 and 3, a main or outer punch 6 is provided and has an internal bore 9 in which an inner or auxiliary punch is provided. An enlarged chamber 10 is provided in the upper enlarged portion of the main punch 6 and a portion of the auxiliary punch 5 is disposed in this chamber and has a collar or radially extending flange 12. A spring 11 is provided in this chamber 10 to urge the auxiliary punch 5 upwardly, however, the punch 5 can be pressed down against the tension of this spring. In this embodiment, the opening 8 of the die 7 is adapted to have an auxiliary die inserted thereinto. This die is provided with an opening 14 which just accommodates the auxiliary punch 5.

In operation, the main punch 6 is brought down onto the surface of the emission foil 1 and the punch 5 is moved downwardly in order to punch a hole in the foil. This is illustrated in FIGURE 2 of the drawing. Next, the die 15 is removed and the cathode holder 2 is inserted in its place as indicated in FIGURE 3. Subsequently, the entire punch 6 is moved downwardly as explained in connection with FIGURE 1 in order to punch out the portion of the foil which surrounds the hole which has already been provided. Thus, a ring-shaped section of the emission foil is punched free from a sheet of foil and is glued or pressed to the upper surface of the cathode holder 2 in the manner indicated in connection with FIGURE 1.

A cathode so produced is ready to be assembled into a system, i.e., the tube into which itis to be provided for use. During the activation process, the barium carbonate (BaCO changes to barium oxide (BaO), and, at the time, this emission coating is tightly sintered onto the surface of the cathode holder.

Cathodes which are manufactured in accordance with the present invention are particularly suitable for use in electron beam tubes such as picture tubes, oscilloscope tubes, travelling wave tubes and similar types of tubes, because these cathodes render it possible to generate an electron beam having a current distribution over its cross section which may be reproduced very Well. Furthermore, the current distribution of the electron beam is very constant during the entire lifetime of the cathode and thus the electron beam tube provided with such a cathode may be manufactured with very small tolerances with respect to the electrical characteristics.

A further use of the cathode of the instant invention is in electron tubes and/or electron beam tubes where low noise levels are desired. The prevention of noise in a travelling wave tube with a low noise level is essentially dependent upon the uniformity of the cathode which generates the beam. The electrons emanating from the edge regions of the cathode in particular influence the noise level of the beam. Since, according to the present invention emission surfaces for cathodes can be manufactured having a roughness at their peripheral edge of less than 10p. (,u=microns=meters and indeed even less than 5,u, these cathodes are particularly suitable for tubes having a low noise level. In this respect it has proven to be advantageous to use an emission material having a conductivity of more than 0.5 ms. mm. (millisiemens times millimeters).

Tubes with cathodes according to the invention have shown noise factors of less than 4 db.

It is to be stated that the film 'or glue and the pressing are used as a means of temporarily holding the foil or tape to the cathode holder. However, the coating adherence of the emissive tape will be improved by applying properly chosen pressure values (typical l0 kg./cm or by using a glue which is bonding the emissive material tightly to the surface of the cathode holder. After or during breakdown of the carbonate coating the coating adherence is due to a chemical reactionbetween the alkaline earth compounds and the material of the cathode holder, which normally consists of nickel. In both mentioned cases of applying the emissive tape to the cathode holder the coating adherence is the better, the better is the mechanical contact between the carbonate grains and the surface of the cathode holder.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. A process for making fiat cathodes for electrical discharge and vacuum tubes and the like, comprising: punching from a sheet of foil containing alkaline earth carbonates a cathode of the required size; and, thereafter, and by means of the element doing the punching, adhering the cathode foil onto the surface of a cathode holder.

2. A process as defined in claim 1 wherein the punching and placing actions are performed in a single continuous working step.

3. A process as defined in claim 2 wherein said foil is placed onto the surface of a cathode holder with sufficient force to press the foil to the holder.

4. A process as defined in claim 2 wherein said foil is glued to the surface of a cathode holder.

5. A process as defined in claim 4 comprising coating the surface of the cathode holder with a non-drying, sticky film of a solution of a synthetic prior to placing the cathode thereon for gluing said cathode in place, said film being decomposable upon subsequent activation of the cathode.

6. A process as defined in claim 5 wherein said film is evaporatable upon cathode activation.

7. A process as defined in claim 5 wherein said film is a solution of poly-isobutylene.

8. A process as defined in claim 5 wherein said film is a solution of polyacrylate.

9. A process as defined in claim 5 wherein said film is a solution of polymethacrylate.

10. A process as defined in claim 5 wherein said film has a thickness of 110,u.

11. A process as defined in claim 2 comprising first punching a hole into the sheet of foil before punching said cathode whereby to make an annular cathode.

12. A process for making flat cathodes having annular I emission surfaces for electrical discharge and vacuum tubes and the like, using a punching device including a removable die, comprising the steps of: punching a hole into a sheet of foil using the punching device and the die; removing said die and inserting a cathode holder in its place; and punching out a portion of the'foil surrounding said hole and, in the same working stroke, adhering it onto the surface of a cathode holder.

13. A process as defined in claim 12 wherein said foil is placed onto the surface of a cathode holder with suf-' ficient force to press the foil to the holder.

14. A process as defined in claim 12 wherein said foil is glued to the surface of a cathode holder.

15. A process for the manufacture of a flat cathode for References Cited by the Examiner UNITED STATES PATENTS 503,966 8/1893 Higgins 83621 1,167,771 1/1916 McCloskey 83621 Luther 83621 Godfrey 156251 Halmrast 83621 Gerrneshausen 313-337 Katz et a1 313337 Klasing et a1. 156251 EARL M. BERGERT, Primary Examiner.

JAMES D. KALLAM, Examiner. 10 A. s. KATZ, D. J. DRUMMOND, Assistant Examiners. 

1. A PROCESS FOR MAKING FLAT CATHODES FOR ELECTRICAL DISCHARGE AND VACUUM TUBES AND THE LIKE COMPRISING: PUNCHING FROM A SHEET OF FOIL CONTAINING ALKALINE EARTH CARBONATES A CATHODE OF THE REQUIRED SIZE; AND, THEREAFTER, AND BY MEANS OF THE ELEMENT DOING THE PUNCHING, ADHERING THE CATHODE FOIL ONTO THE SURFACE OF A CATHODE HOLDER. 